U.S. patent application number 16/075842 was filed with the patent office on 2019-02-14 for integrated one-piece polarizing interferometer and snapshot spectro-polarimeter applying same.
The applicant listed for this patent is INDUSTRIAL COOPERATION FOUNDATION CHONBUK NATIONAL UNIVERSITY. Invention is credited to Dae Suk KIM.
Application Number | 20190049302 16/075842 |
Document ID | / |
Family ID | 59499636 |
Filed Date | 2019-02-14 |
![](/patent/app/20190049302/US20190049302A1-20190214-D00000.png)
![](/patent/app/20190049302/US20190049302A1-20190214-D00001.png)
![](/patent/app/20190049302/US20190049302A1-20190214-D00002.png)
![](/patent/app/20190049302/US20190049302A1-20190214-D00003.png)
![](/patent/app/20190049302/US20190049302A1-20190214-D00004.png)
![](/patent/app/20190049302/US20190049302A1-20190214-D00005.png)
![](/patent/app/20190049302/US20190049302A1-20190214-D00006.png)
![](/patent/app/20190049302/US20190049302A1-20190214-M00001.png)
![](/patent/app/20190049302/US20190049302A1-20190214-M00002.png)
United States Patent
Application |
20190049302 |
Kind Code |
A1 |
KIM; Dae Suk |
February 14, 2019 |
INTEGRATED ONE-PIECE POLARIZING INTERFEROMETER AND SNAPSHOT
SPECTRO-POLARIMETER APPLYING SAME
Abstract
An integrated one-piece polarizing interferometer includes a
polarization beam splitter for separating incident complex waves, a
first mirror attached to a first surface of the polarization beam
splitter, for reflecting a first polarization transmitted through
the polarization beam splitter to the polarization beam splitter,
and a second mirror attached to a second surface of the
polarization beam splitter, for reflecting a second polarization
transmitted through the polarization beam splitter to the
polarization beam splitter. Accordingly, it is possible to measure
dynamic spectroscopic polarization phenomenon with extremely high
robustness disturbances due to an external vibration and the like
by using the integrated one-piece polarizing interferometer,
thereby improving measurement repeatability and accuracy of
measurement.
Inventors: |
KIM; Dae Suk; (Jeollabuk-do,
KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
INDUSTRIAL COOPERATION FOUNDATION CHONBUK NATIONAL
UNIVERSITY |
Jeollabuk-do |
|
KR |
|
|
Family ID: |
59499636 |
Appl. No.: |
16/075842 |
Filed: |
January 26, 2017 |
PCT Filed: |
January 26, 2017 |
PCT NO: |
PCT/KR2017/000934 |
371 Date: |
September 7, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01N 2201/0683 20130101;
G01J 3/447 20130101; G02B 27/283 20130101; G01J 3/0256 20130101;
G01J 3/45 20130101; G01J 3/08 20130101; G01J 3/4532 20130101; G01N
21/27 20130101; G01N 21/01 20130101; G02B 27/28 20130101; G01J
3/0224 20130101; G01J 3/4531 20130101; G01N 21/21 20130101; G01J
3/0232 20130101; G01N 2021/213 20130101 |
International
Class: |
G01J 3/45 20060101
G01J003/45; G01N 21/21 20060101 G01N021/21; G01N 21/27 20060101
G01N021/27; G02B 27/28 20060101 G02B027/28 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 4, 2016 |
KR |
10-2016-0013928 |
Claims
1. An integrated one-piece polarizing interferometer comprising: a
polarizing beam splitter configured to split incident complex
waves; a first mirror attached to a first surface of the polarizing
beam splitter and configured to reflect, to the polarizing beam
splitter, first polarized light passing through the polarizing beam
splitter; and a second mirror attached to a second surface of the
polarizing beam splitter and configured to reflect, to the
polarizing beam splitter, second polarized light reflected by the
polarizing beam splitter.
2. The integrated one-piece polarizing interferometer of claim 1,
wherein an optical path length of the first polarized light differs
from an optical path length of the second polarized light in the
integrated one-piece polarizing interferometer.
3. The integrated one-piece polarizing interferometer of claim 2,
wherein the first mirror is attached to the polarizing beam
splitter directly or with a spacer disposed therebetween, and
wherein the second mirror is attached to the polarizing beam
splitter directly or with a spacer disposed therebetween.
4. The integrated one-piece polarizing interferometer of claim 3,
wherein the difference between the optical path length of the first
polarized light and the optical path length of the second polarized
light ranges from 20 .mu.m to 60 .mu.m for an ultraviolet or
visible light region and 60 .mu.m to 500 .mu.m for a near-infrared
or infrared region.
5. The integrated one-piece polarizing interferometer of claim 4,
wherein the first polarized light is P-polarized light, and the
second polarized light is S-polarized light.
6. A snapshot spectro-polarimeter comprising: a first linear
polarizer configured to linearly-polarize light emitted from a
light source; the integrated one-piece polarizing interferometer of
claim 1 to polarization-modulate complex waves that are output from
the first linear polarizer and pass through, or are reflected by,
an object; a second linear polarizer configured to cause two waves
output from the integrated one-piece polarizing interferometer to
interfere with each other; and a measurement device configured to
measure spectrum polarization information of light output from the
second linear polarizer.
7. The snapshot spectro-polarimeter of claim 6, wherein the first
linear polarizer and the second linear polarizer are linear
polarizers oriented in the same direction.
8. The snapshot spectro-polarimeter of claim 6, wherein an optical
path length of the first polarized light differs from an optical
path length of the second polarized light in the integrated
one-piece polarizing interferometer.
9. The snapshot spectro-polarimeter of claim 6, wherein a
measurement wavelength region of the measurement device comprises
at least one of a visible light region, an ultraviolet region, a
near-infrared region, and an infrared region.
10. An integrated one-piece polarizing interferometer comprising: a
beam splitter configured to split incident complex waves; a first
polarizer attached to a first surface of the beam splitter and
configured to polarize light passing through the beam splitter; a
first mirror configured to reflect, to the beam splitter, first
polarized light output from the first polarizer; a second polarizer
attached to a second surface of the beam splitter to polarize light
reflected by the beam splitter; and a second mirror configured to
reflect, to the beam splitter, second polarized light output from
the second polarizer.
11. A snapshot spectro-polarimeter comprising: a linear polarizer
configured to linearly-polarize light emitted from a light source;
an integrated one-piece polarizing interferometer configured to
modulate polarized light input from the linear polarizer; a beam
splitter configured to split interference waves modulated by the
integrated one-piece polarizing interferometer into two paths; a
chopper wheel configured to periodically transmit first light split
by the beam splitter to an object and periodically transmit second
light split by the beam splitter to a path in which there is no
object; and a measurement device configured to measure spectral
polarization information of the first light and the second light,
wherein the integrated one-piece polarizing interferometer
comprises: a polarizing beam splitter configured to split polarized
light input from the linear polarizer; a first mirror attached to a
first surface of the polarizing beam splitter to reflect, to the
polarizing beam splitter, first polarized light passing through the
polarizing beam splitter; and a second mirror attached to a second
surface of the polarizing beam splitter to reflect, to the
polarizing beam splitter, second polarized light reflected by the
polarizing beam splitter.
12. The snapshot spectro-polarimeter of claim 11, wherein a
measurement wavelength region of the measurement device comprises
at least one of a visible light region, an ultraviolet region, a
near-infrared region, and an infrared region.
13. A snapshot spectro-polarimeter comprising: a linear polarizer
configured to linearly-polarize light emitted from a light source;
the integrated one-piece polarizing interferometer of claim 1 to
modulate polarized light input from the linear polarizer; a beam
splitter configured to split interference waves modulated by the
integrated one-piece polarizing interferometer; a first measurement
device configured to measure spectral polarization information of
first light that is split by the beam splitter and passes through,
or is reflected by, an object; and a second measurement device
configured to measure spectral polarization information of second
light that is split by the beam splitter and does not pass through,
or is not reflected by, the object.
14. The snapshot spectro-polarimeter of claim 13, wherein
measurement wavelength regions of the first measurement device and
the second measurement device comprise at least one of a visible
light region, an ultraviolet region, a near-infrared region, and an
infrared region.
Description
CROSS REFERENCE TO RELATED APPLICATIONS AND CLAIM OF PRIORITY
[0001] This application claims benefit under 35 U.S.C. 119(e), 120,
121, or 365(c), and is a National Stage entry from International
Application No. PCT/KR2017/000934, filed Jan. 26, 2017, which
claims priority to the benefit of Korean Patent Application No.
10-2016-0013928 filed in the Korean Intellectual Property Office on
Feb. 4, 2016, the entire contents of which are incorporated herein
by reference.
TECHNICAL FIELD
[0002] The present invention relates to a spectro-polarimeter and a
polarizing interferometer applicable thereto, and more
particularly, to a spectro-polarimeter that rapidly measures a
spectral Stokes vector that represents spectral polarization
information of light that passes through or is reflected by an
object being measured, and a polarizing interferometer applied
thereto.
BACKGROUND ART
[0003] Spectropolarimetry is one of the most accurate solutions
applicable to various fields. Some studies have been conducted to
combine interferometry with polarimetry such as spectral domain
polarization-sensitive optical coherence tomography (SD PS-OCT),
real-time high-sensitivity surface-plasmon resonance (SPR)
bio-sensing, circular dichroism (CD) measurement, and the like.
[0004] Typical spectropolarimetric system in the related art
employs a mechanical rotating mechanism or an electrical modulation
element to obtain spectroscopic ellipsometric parameters .PSI.(k)
and .DELTA.(k) for deriving the spectral Stokes vector and has a
disadvantage of requiring measurement time of seconds or much
longer periods. To solve the problem of time-consuming measurement
approach, snapshot-based interferometric spectropolarimetry has
been developed. However, since the conventional snapshot technology
is based on the principle of a traditional interferometer employing
multiple-piece of optical scheme, the preciously proposed
snapshot-based spectropolarimetry may be used to perform a snapshot
measurement capability, but may be vulnerable to disturbances
caused by external vibration. Hence, the snapshot-based
spectropolarimetry may not provide high precision of measurement
repeatability and stability that the conventional
spectropolarimetry based on the mechanically rotating polarization
modulation type or the electrical modulation type can provide.
SUMMARY
[0005] The present invention is directed to providing an integrated
one-piece polarizing interferometer that is highly robust to
disturbances caused by external vibration, and a snapshot
spectro-polarimeter employing the same.
[0006] One aspect of the present invention provides an integrated
one-piece polarizing interferometer that includes a polarizing beam
splitter that splits incident complex waves, a first mirror
attached to a first surface of the polarizing beam splitter and
reflecting, to the polarizing beam splitter, first polarized light
passing through the polarizing beam splitter, and a second mirror
attached to a second surface of the polarizing beam splitter and
reflecting, to the polarizing beam splitter, second polarized light
reflected by the polarizing beam splitter.
[0007] An optical path length of the first polarized light may
differ from an optical path length of the second polarized light in
the integrated one-piece polarizing interferometer.
[0008] A gap between the polarizing beam splitter and the first
mirror may differ from a gap between the polarizing beam splitter
and the second mirror.
[0009] The difference between the optical path length of the first
polarized light and the optical path length of the second polarized
light may range from 20 .mu.m to 60 .mu.m for an ultraviolet or
visible light region and 60 .mu.m to 500 .mu.m for a near-infrared
or infrared region.
[0010] The first polarized light may be P-polarized light, and the
second polarized light may be S-polarized light.
[0011] Another aspect of the present invention provides a snapshot
spectro-polarimeter that includes a first linear polarizer that
linearly-polarizes light emitted from a light source, an integrated
one-piece polarizing interferometer that polarization-modulates
light that is output from the first linear polarizer and passes
through an object, a second linear polarizer that causes two waves
output from the integrated one-piece polarizing interferometer to
interfere with each other, and a measurement device that measures
spectral polarization information of light output from the second
linear polarizer. The integrated one-piece polarizing
interferometer includes a polarizing beam splitter that splits
incident complex waves, a first mirror attached to a first surface
of the polarizing beam splitter directly or with a spacer disposed
therebetween and reflecting, to the polarizing beam splitter, first
polarized light passing through the polarizing beam splitter, and a
second mirror attached to a second surface of the polarizing beam
splitter directly or with a spacer disposed therebetween and
reflecting, to the polarizing beam splitter, second polarized light
reflected by the polarizing beam splitter.
[0012] The first linear polarizer and the second linear polarizer
may be linear polarizers oriented at 45.degree..
[0013] An optical path length of the first polarized light may
differ from an optical path length of the second polarized light in
the integrated one-piece polarizing interferometer. A gap between
the polarizing beam splitter and the first mirror may differ from a
gap between the polarizing beam splitter and the second mirror.
[0014] Another aspect of the present invention provides an
integrated one-piece polarizing interferometer that includes a beam
splitter that splits incident complex waves, a first polarizer
attached to a first surface of the beam splitter and polarizing
light passing through the beam splitter, a first mirror that
reflects, to the beam splitter, first polarized light output from
the first polarizer, a second polarizer attached to a second
surface of the beam splitter and polarizing light reflected by the
beam splitter, and a second mirror that reflects, to the beam
splitter, second polarized light output from the second
polarizer.
[0015] Another aspect of the present invention provides a snapshot
spectro-polarimeter that includes a linear polarizer that
linearly-polarizes light emitted from a light source, an integrated
one-piece polarizing interferometer that modulates polarized light
input from the linear polarizer, a beam splitter that splits
interference waves modulated by the integrated one-piece polarizing
interferometer into two paths, a chopper wheel that periodically
transmits first light split by the beam splitter to an object and
periodically transmits second light split by the beam splitter to a
path in which there is no object, and a measurement device that
measures spectrum polarization information of the first light and
the second light. The integrated one-piece polarizing
interferometer includes a polarizing beam splitter that splits
polarized light input from the linear polarizer, a first mirror
attached to a first surface of the polarizing beam splitter and
reflecting, to the polarizing beam splitter, first polarized light
passing through the polarizing beam splitter, and a second mirror
attached to a second surface of the polarizing beam splitter and
reflecting, to the polarizing beam splitter, second polarized light
reflected by the polarizing beam splitter.
[0016] Another aspect of the present invention provides a snapshot
spectro-polarimeter that includes a linear polarizer that
linearly-polarizes light emitted from a light source, an integrated
one-piece polarizing interferometer that modulates polarized light
input from the linear polarizer, a beam splitter that splits
interference waves modulated by the integrated one-piece polarizing
interferometer, a first measurement device that measures spectral
polarization information of first light that is split by the beam
splitter and passes through, or is reflected by, an object, and a
second measurement device that measures spectral polarization
information of second light that is split by the beam splitter and
does not pass through, or is not reflected by, the object. The
integrated one-piece polarizing interferometer includes a
polarizing beam splitter that splits polarized light input from the
linear polarizer, a first mirror attached to a first surface of the
polarizing beam splitter and reflecting, to the polarizing beam
splitter, first polarized light passing through the polarizing beam
splitter, and a second mirror attached to a second surface of the
polarizing beam splitter and reflecting, to the polarizing beam
splitter, second polarized light reflected by the polarizing beam
splitter.
[0017] According to embodiments of the present invention, an
integrated one-piece polarizing interferometer enables measurement
of a spectral polarization phenomenon dynamically with extremely
high robustness to disturbances caused by external vibration,
thereby improving measurement repeatability and accuracy while
having the dynamic measurement capability.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a diagram illustrating a snapshot
spectro-polarimeter using an integrated one-piece polarizing
interferometer according to an embodiment of the present
invention.
[0019] FIG. 2 is a diagram illustrating an integrated one-piece
polarizing interferometer according to another embodiment of the
present invention.
[0020] FIG. 3 illustrates spectral interference data measured by a
single spectrum sensing module in the absence of an object.
[0021] FIG. 4 illustrates results obtained by measuring a spectral
polarimetric phase difference .DELTA..sub.a(k) by rotating a
quarter wave plate (QWP) placed at the object position every
10.degree..
[0022] FIG. 5 is a diagram illustrating a snapshot
spectropo-larimeter using an integrated one-piece polarizing
interferometer according to another embodiment of the present
invention.
[0023] FIG. 6 is a diagram illustrating a snapshot
spectro-polarimeter using an integrated one-piece polarizing
interferometer according to still another embodiment of the present
invention.
[0024] FIG. 7 is a structural view of a chopper wheel illustrated
in FIG. 6.
[0025] FIG. 8 is a diagram illustrating a snapshot
spectro-polarimeter using an integrated one-piece polarizing
interferometer according to another embodiment of the present
invention.
[0026] FIG. 9 is a graph depicting results obtained by measuring a
spectral polarimetric phase difference .DELTA..sub.a(k) of a 500-nm
silicon oxide thin-film object using the configuration illustrated
in FIG. 8.
DETAILED DESCRIPTION
[0027] Hereinafter, the present invention will be described in more
detail with reference to the accompanying drawings.
[0028] FIG. 1 is a diagram illustrating a snapshot
spectro-polarimeter using an integrated one-piece polarizing
interferometer according to an embodiment of the present
invention.
[0029] The snapshot spectro-polarimeter according to an embodiment
of the present invention is a system for performing fast and
real-time measurement of a spectral Stokes vector, which represents
spectral polarization information of an object 160 being measured,
by a snapshot method.
[0030] The snapshot spectro-polarimeter according to the embodiment
of the present invention does not use a mechanically rotating
mechanism or an electrical modulation element, and may measure the
spectral Stokes vector, which has information about multiple
wavelengths, in real time with only a single spectral interference
data.
[0031] As illustrated in FIG. 1, the snapshot spectro-polarimeter
according to the embodiment of the present invention includes a
light source 110, a light source fiber 120, a collimating lens 130,
a linear polarizer (LP) 140, an iris 150, a beam splitter (BS) 170,
a polarization modulation module (PMM) 180, and a linear polarizer
(LP) 190.
[0032] A white light source is used as the light source 110. For
example, a 100 W tungsten-halogen lamp may be used as the light
source 110. However, various other types of light sources may also
be used as the light source 110.
[0033] Light emitted from the light source 110 is transmitted to
the light source fiber 120 and then converted into collimated light
by the collimating lens 130. The collimated light is linearly
polarized at an angle of 45.degree. by the LP 140. The iris 150
adjusts the magnitude of the linearly-polarized light passing
through the LP 140.
[0034] The linearly-polarized light adjusted to have an appropriate
magnitude by the iris 150 passes through the anisotropic
transmissive object 160 being measured, passes through the BS 170,
and then enters the PMM 180.
[0035] The PMM 180 is an integrated one-piece polarizing
interferometer that polarization-modulates waves passing through
the object 160. As illustrated in FIG. 1, the PMM 180 includes a
polarizing beam splitter (PBS) 181 and mirrors 183 and 185.
[0036] The PBS 181 splits incident complex waves. P-polarized light
passes through PBS 181 and is incident on the mirror 183, and
S-polarized light is reflected by the PBS 181 and is incident on
the mirror 185.
[0037] The mirrors 183 and 185 are fixedly attached to the PBS 181.
Specifically, the mirror 183 is attached to a side surface of the
PBS 181 and reflects the P-polarized light passing through the PBS
181, and the mirror 185 is attached to a bottom surface of the PBS
181 and reflects the S-polarized light reflected by the PBS
181.
[0038] To generate a high-frequency signal in a spectrum
polarization signal, it is needed to generate the difference in
optical path length between the P-polarized light, which passes
through the PBS 181, is reflected by the mirror 183, and then
passes through the PBS 181 in the PMM 180, and the S-polarized
light, which is reflected by the PBS 181 and the mirror 185 and
then reflected again by the PBS 181. That is, one optical path
length is longer than the other optical path length. For example,
the one optical path length may be longer than the other optical
path length by 20 .mu.m to 60 .mu.m when the measurement wavelength
region corresponds to an ultraviolet region or a visible light
region and by 60 .mu.m to 500 .mu.m when the measurement wavelength
region corresponds to a near-infrared region or an infrared
region.
[0039] The optical path length of the P-polarized light may be
longer than that of the S-polarized light, or the optical path
length of the S-polarized light may be longer than that of the
P-polarized light.
[0040] To make the optical path length difference, the gap between
the PBS 181 and the mirror 183 differs from the gap between the PBS
181 and the mirror 185. That is, one of the mirrors 183 and 185 is
farther away from the PBS 181 than the other. The one mirror is
farther away from the PBS 181 than the other mirror by 20 .mu.m to
60 .mu.m when the measurement wavelength region corresponds to the
ultraviolet region or the visible light region and by 60 .mu.m to
500 .mu.m when the measurement wavelength region to corresponds to
the near-infrared region or the infrared region.
[0041] For the gap difference of 20 .mu.m to 60 .mu.m or 60 .mu.m
to 500 .mu.m, the two mirrors 183 and 185 may be accurately
arranged to have the suitable optical path difference of 20 .mu.m
to 60 .mu.m or 60 .mu.m to 500 .mu.m, or a spacer having a
thickness corresponding to the optical path difference may be
inserted between the mirrors 183 and 185.
[0042] Meanwhile, the PMM 180 may be implemented with a combination
of a non-polarizing beam splitter (NPBS), two polarizers, and two
mirrors, rather than the combination of the PBS 181 and the two
mirrors 183 and 185. Such a combination is illustrated in FIG.
2.
[0043] FIG. 2 illustrates a structure in which the PBS 181
illustrated in FIG. 1 is replaced with a combination of two LPs 187
and 188, the polarization directions of which are perpendicular to
each other, integrally attached to two beam paths split by an NPBS
186. The PBS may have a limitation in precise polarization
measurement performance because the PBS has a limited polarization
extinction ratio of about 1/1000. Therefore, the PBS may be
replaced with the combination of the NPBS and the two polarizers,
resulting in a high extinction ratio.
[0044] Mirrors 183 and 185 are fixedly attached to the LPs 187 and
188, respectively, and in order to make an optical path length
difference, a gap between the LP (P-polarization direction) 187 and
the mirror 183 differs from a gap between the LP (S-polarization
direction) 188 and the mirror 185.
[0045] The following description will be given with reference to
FIG. 1.
[0046] The two waves polarization-modulated by the PMM 180 are
reflected by the BS 170 and then linearly polarized at an angle of
45.degree. by the LP 190 to interfere with each other. The
interference waves enter a single spectrum sensing module (not
illustrated). The single spectrum sensing module may be a
spectrometer of a sensor array type.
[0047] The LP 140 included in the snapshot spectro-polarimeter
according to an embodiment of the present invention is a component
for improving contrast of light interference.
[0048] The single spectrum sensing module measures a spectral
Stokes vector, which represents spectrum polarization information
of an anisotropic transmissive element, by a snapshot method.
[0049] Hereinafter, an interference phenomenon caused by
polarization modulation in the integrated one-piece polarizing
interferometer, which is implemented with the PMM 180, will be
described in detail using the following equations.
[0050] Spectrum polarization information measured by the single
spectrum sensing module may be represented by Equation 1.
I.sub.45.degree.(k)=(E.sub.p.sub._.sub.45.degree.(k)+E.sub.s.sub._.sub.4-
5.degree.(k))(E.sub.p.sub._.sub.45.degree.(k)+E.sub.s.sub._.sub.45.degree.-
(k)) (1)
[0051] Here, a wave number k is equal to 2.pi./.lamda., and
E.sub.p.sub._.sub.45.degree.(k) and E.sub.s.sub._.sub.45.degree.(k)
are 45.degree. components for complex waves of E.sub.p(k) and
E.sub.s(k) that are represented by Equation 2.
E p ( k ) = B NP B P B NP E in ( k ) e ikz D = 1 2 B NP [ 1 0 ] B
NP E in ( k ) e ikz p E s ( k ) = B NP B P B NP E in ( k ) e ikz D
= 1 2 B NP [ 0 1 ] B NP E in ( k ) e ikz s ( 2 ) ##EQU00001##
[0052] Here, E.sub.in(k) represents input waves at an entrance of
the integrated one-piece polarizing interferometer. E.sub.p(k) is
P-polarized light that passes through the PBS 181 and is reflected
by the mirror 183, and E.sub.s(k) is S-polarized light that is
reflected by the PBS 181 and the mirror 185. z.sub.p and z.sub.s
represent optical path lengths of the P-polarized light and the
S-polarized light in the integrated one-piece polarizing
interferometer, respectively.
[0053] Meanwhile, a spectrum interference signal in the absence of
the object 160 is represented by Equation 3.
I.sub.45.sup.no.sup._.sup.object(k)=|E.sub.p.sub._.sub.45.degree.|.sup.2-
+|E.sub.s.sub._.sub.45.degree.|2.gamma.|E.sub.p.sub._.sub.45.degree..paral-
lel.E.sub.s.sub._.sub.45.degree.| cos
[.PHI..sup.no.sup._.sup.object(k)] (3) [0054] Here,
.PHI..sup.no.sup._.sup.object(k)=kz.sub.0+[.xi.(k)-.eta.(k)]
[0055] Here, z.sub.0=|z.sub.p-z.sub.s| is an optical path length
difference. The optical path difference between z.sub.p and z.sub.s
generates high-frequency spectral interference that is required to
obtain a spectral polarimetric phase by using a snapshot scheme.
The spectral polarimetric phase function
.PHI..sup.no.sup._.sup.object(k) may be derived using Fourier
transform technique or direct phase calculation that is applied to
the spectral domain.
[0056] A spectral interference signal in the presence of the object
160 is represented by Equation 4.
I.sub.45.sup.object(k)=|E.sub.p.sub._.sub.45.degree.|.sup.2+|E.sub.s.sub-
._.sub.45.degree.|2.gamma.|E.sub.p.sub._.sub.45.degree..parallel.E.sub.s.s-
ub._.sub.45.degree.| cos [.PHI..sup.object(k)] (4) [0057] Here,
.PHI..sup.object(k)=kz.sub.0+[.xi.(k)-.eta.(k)]+[.delta..sub.p(k)-.delta.-
.sub.s(k)]
[0058] For a case in which the transmissive object 16 is not
present and a case in which the transmissive object 16 is present,
incident waves E.sub.in(k) at the entrance of the integrated
one-piece polarizing interferometer are represented by Equation
5.
E in no _ object ( k ) = [ u ( k ) e i .xi. ( k ) v ( k ) e i .eta.
( k ) ] , E in object ( k ) = [ u ( k ) t p e i [ .xi. ( k ) +
.delta. p ( k ) ] v ( k ) t s e i [ .eta. ( k ) + .delta. s ( k ) ]
] ( 5 ) ##EQU00002##
[0059] The spectral polarimetric phase function .PHI..sup.object(k)
may be derived using the aforementioned Fourier transform
technique. The spectral polarimetric phase difference
.DELTA..sub.a(k) caused by the object 160 is calculated by
subtracting .PHI..sup.no.sup._.sup.object(k) from
.PHI..sup.object(k), as in Equation 6.
.DELTA..sub.a(k)=.delta..sub.p(k)-+.delta..sub.s(k)=.PHI..sup.object(k)--
.PHI..sup.no.sup._.sup.object(k) (6)
[0060] FIG. 3 illustrates spectral interference data measured by
the single spectrum sensing module when the object 160 is not
present, and FIG. 4 illustrates results obtained by measuring the
spectral polarimetric phase difference .DELTA..sub.a(k) by rotating
a quarter wave plate (QWP) placed at the object 160 position every
10.degree..
[0061] In FIG. 4, the solid line represents measurement results
obtained by using a technique according to an embodiment of the
present invention, and the dotted line represents measurement
results obtained using a commercial mechanical polarization element
type system. It can be seen that there is no significant difference
therebetween.
[0062] FIG. 5 is a diagram illustrating a snapshot
spectro-polarimeter using an integrated one-piece polarizing
interferometer according to another embodiment of the present
invention.
[0063] The snapshot spectro-polarimeter illustrated in FIG. 5
structurally differs from the system illustrated in FIG. 1 in that
the former is a system for measuring spectral polarization
information about a reflective sample such as a nano pattern, a
roll nano pattern, and the like, whereas the latter is a system for
measuring spectral polarization information about a transmissive
sample.
[0064] Among components illustrated in FIG. 5, a light source 210,
a light source fiber 220, a collimating lens 230, an LP 240, a PMM
270, and an LP 280 may be implemented to be equivalent to,
respectively, the light source 110, the light source fiber 120, the
collimating lens 130, the LP 140, the PMM 180, and the LP 190
illustrated in FIG. 1.
[0065] A lens 261 and NPBSs 263 and 265 are components for
transmitting light linearly polarized by the LP 240 to a reflective
object 250 being measured, allowing complex waves output from the
reflective object 250 to enter the PMM 270, and allowing two waves
polarization-modulated by the PMM 270 to enter the LP 280.
[0066] The two waves entering the LP 280 are linearly polarized at
an angle of 45.degree. to interfere with each other, and the
interference waves enter a spectrometer 300 through a lens 290.
[0067] The exemplary embodiments of the snapshot
spectro-polarimeters using the integrated one-piece polarizing
interferometers have hitherto been described in detail.
[0068] The spectral polarimetric phase difference .DELTA..sub.a(k)
caused by the object 160 in FIG. 1 is calculated by subtracting
.PHI..sup.no.sup._.sup.object(k) from .PHI..sup.object(k), as in
Equation 6. That is, the spectral polarimetric phase difference
.DELTA..sub.a(k), which is an accurate spectral polarimetric phase
difference of an object being measured, may be obtained by
performing compensation using the measurement results in the
absence of the object.
[0069] However, since the spectral polarimetric phase function
.PHI..sup.no.sup._.sup.object(k) in the absence of an object is
slightly changed by disturbances such as a temperature change in
the atmosphere, environment control, such as isothermal-isohumidity
control, is required for high-precision measurement.
[0070] To perform stable precision measurement which highly robust
to disturbances in general environmental condition in which an
isothermal-isohumidity control system is not present, it is
necessary to simultaneously measure
.PHI..sup.no.sup._.sup.object(k) in the absence of an object and
.PHI..sup.object(k) in the presence of an object, rather than
measuring .PHI..sup.no.sup._.sup.object(k) only once since
.PHI..sup.no.sup._.sup.object(k) can be varied by external
temperature change.
[0071] FIG. 6 is a diagram illustrating a snapshot
spectro-polarimeter that is capable of achieving measurement
accuracy and repeatability of an integrated one-piece polarizing
interferometer even in general environmental condition. The
snapshot spectro-polarimeter according to the embodiment of the
present invention consecutively measures .PHI..sup.object(k) and
.PHI..sup.no.sup._.sup.object(k) by rotating a chopper wheel 194 at
constant speed using a motor, rather than separately performing the
measurement for the case in which an object is present and the
measurement for the case in which an object is not present. The
spectral polarimetric phase difference .DELTA..sub.a(k) is obtained
by almost simultaneously measuring .PHI..sup.object(k) and
.PHI..sup.no.sup._.sup.object(k) while rotating the chopper wheel
194 at a rotational speed of about 30 to 60 rounds per minute
(RPM).
[0072] As illustrated in FIG. 6, in order to achieve the above
operations, interference waves modulated by the integrated
one-piece polarizing interferometer are split into two paths by a
beam splitter (NPBS) 191. A transmissive object 160 to be measured
is located in one path, and there is no object in the other path
reflected by a mirror 192.
[0073] Light passing through the object 160 is reflected by a
mirror 195 and then reflected by an NPBS 196 and enters a
spectrometer through a lens 197. The remaining light, which does
not pass through the object 160, passes through the NPBS 196 and
enters the spectrometer through the lens 197.
[0074] Meanwhile, as can be seen from the structure of the chopper
wheel 194 in FIG. 7, when only an interference wave signal in one
path enters the spectrometer, the snapshot spectro-polarimeter may
measure .PHI..sup.no.sup._.sup.object(k) when the chopper wheel 914
is rotated through one revolution by a motor 193. For example,
assuming that the chopper wheel 914 rotates one revolution per
second, light not passing through the object 160 periodically
enters the spectrometer every one second to allow measurement of
.PHI..sup.no.sup._.sup.object(k), thereby resulting in high
robustness to slowly changed external disturbances, such as a
temperature change.
[0075] Although the embodiment of the present invention is related
to a transmissive object, the same method may also be applied to a
reflective object with a normal incidence or any specific incidence
angle.
[0076] FIG. 8 illustrates a snapshot spectro-polarimeter capable of
achieving performance of a high-precision integrated one-piece
polarizing interferometer in a normal environment, according to
another embodiment of the present invention. Provided is a method
for simultaneously measuring spectral polarization-modulated
signals based on two spectrometers 310 and 320, instead of using
the chopper wheel scheme.
[0077] Although a reflective object 255 with an incidence angle of
45.degree. is used in the embodiment of the present invention, the
same method may also be applied to a transmissive object, a
normal-incidence reflective object based on the two spectrometers
310 and 320, or a reflective object of a specific incidence
angle.
[0078] In the embodiment of the present invention, interference
waves output through the integrated one-piece polarizing
interferometer are split into two paths by a beam splitter (NPBS)
275 located in front of a thin-film object to be measured at an
incidence angle of 45.degree.. In one path,
.PHI..sup.no.sup._.sup.object(k) is measured after interference
waves not being reflected by the object 255 are obtained using the
spectrometer 1 310, and in the other path, .PHI..sup.object(k) is
measured after interference waves reflected by the object 255 are
obtained using the spectrometer 2 320.
[0079] FIG. 9 illustrates results obtained by measuring a spectral
polarimetric phase difference .DELTA..sub.a(k) of a 500-nm silicon
oxide thin-film using the configuration illustrated in FIG. 8,
wherein the measured result matches well with that measured by a
commercial spectro-polarimeter shown by a dotted line. An optical
system in a visible light region is used in the embodiment of the
present invention, and only a part of the results for the
wavelength range of 443 nm to 730 nm is compared with the results
of the commercial product.
[0080] The visible light region of 443 nm to 730 nm, described
above as a measurement wavelength region, is merely illustrative.
It should be understood that the spirit of the present invention
may also be applied to an ultraviolet region of 200 nm to 400 nm
and a near-infrared and infrared regions of about 700 nm to 25
microns.
[0081] Although the exemplary embodiments of the present invention
have been described above, the present invention is not limited to
the above-described specific embodiments, and those skilled in the
art will appreciate that various modifications, additions, and
substitutions are possible, without departing from the scope and
spirit of the invention as disclosed in the accompanying claims. In
addition, these modifications and variations should not be
understood separately from the technical ideas or prospects of the
present invention.
* * * * *